Semiconductive magnetic transducer

ABSTRACT

A region for injection of minority carriers is provided at one end of an extended semiconductive channel which is contiguous along one side with a collector region, and an electric field is provided in the channel such that a magnetic field applied substantially perpendicular to the channel preferentially deflects minority carriers to or from the collector.

United States Patent Kurt Lehovec Williamstown, Mass. 775,240

Nov. 13, 1968 June 15, 1971 Sprague Electric Company North Adams, Mass.

Inventor Appl. No. Filed Patented Assignee SEMICONDUCTIVE MAGNETICTRANSDUCER 11 Claims, 9 Drawing Figs.

Int. Cl 1101111/00 Field of Search 317/235,

[56] References Cited UNITED STATES PATENTS 2,778,956 1/1957 Dacey eta1. 317/235 2,943,269 6/1960 Huang 317/235 3,389,230 6/1968 Hudson317/235 3,401,319 9/1968 Watkins 317/235 Primary Examiner-Jerry D. CraigAttorneys-Connolly and Hutz, Vincent H. Sweeney, James P.

OSullivan and David R. Thornton PATENTED JUN! 51971 SEMICONDUCTIVEMAGNETIC TRANSDUCER BACKGROUND OF THE INVENTION This invention relatesto magnetic transducers and more particularlyto a semiconductivemagnetic transducer having an elongated semiconductive channel.

Magnetic transducers which are perhaps best known for their applicationin tape recorders, find many applications in modern electronics,including switching applications and the like. In the prior art,semiconductive magnetic transducers, which utilize magnetic deflectionof minority carriers of a baselike semiconducting region to pointcontact collectors or to an underlying pair of collector regions, isavailable. However, devices of this type are generally low insensitivity and limited in their application.

It is an object of this invention to provide a highly sensitivesemiconductive magnetic transducer.

It is another object of this invention to provide a magnetic transducerhaving an elongated channel contiguous along one side with a collectorregion.

It is still another object of this invention to provide a magnetictransducer having an electric field disposed in an elongatedsemiconductive channel so as to enhance the flow of minority carriersalong the channel.

It is a further object of this invention to provide a semiconductivemagnetic transducer in combination with semiconductive regions whichprovide amplifying characteristics.

It is a still further object of this invention to provide asemiconductive magnetic transducer which also provides unipolar andbipolar characteristics.

SUMMARY OF THE INVENTION Broadly, a semiconductive magnetic transducerprovidedin accordance with the invention comprises an elongatedsemiconductive channel bounded on one side by a collector region ofminority carriers, means disposed at one end of said channel forinjection of minority carriers therein, and said channel having anelectric field therein of such polarity as to direct the minoritycarrier flow along the axis of said channel such that a magnetic fieldapplied across the channel will deflect said drifting minority carriersand control their collection in said collector region.

Broadly, a magnetic transducer-amplifier providedin accordance with theinvention comprises a body of semiconductor material, a semiconductivechannel in said body, at least one collector region of said bodyadjoining said channel, means for injecting minority carriers in saidchannel, an amplifying unit disposed in said body with its input coupledto said collector such that the output of said amplifyingdevice isproportional to the minority carrier flow to said collector.

In a more limited sense, the transducer-amplifier includesa feedbackwithin said body from said amplifying device such that minority carrierflow is increased. This is accomplished in one embodiment by making saidcollector also operate as source of majority carriers of said channelwhich thereby increases the minority carrier injection and flow of saidchannel.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a view in section of asemiconductive magnetic transducer provided in accordance with theinvention;

FIG. 2 is a view in section of another embodiment of the inventionwherein an electric field of the channel is provided by externallycharged contacts at opposing ends of the channel;

FIG. 3 is a plan view of the semiconducting structure .of FIG. 2;

FIG. 4 is a view in section of another embodiment which provides asemiconductive channel parallel to the wafer surface;

FIG. 5 is a graph of the lateral impurity distribution in the channel ofthe structure of FIG. 4;

FIG. 6 is a view in section of still another embodiment of the inventionwherein a collector of the device is provided by a Schottky barriercontact;

FIG. 7 shows a further embodiment of the invention wherein a collectorof the device is provided by an inversion layer region;

FIG. 8 is a view in section of a transducer-amplifier provided inaccordance with the invention; and

FIG. 9 is a view in section of a further embodiment wherein a transducerand an MOS amplifier are integrally combined.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to provide a clear andconcise description of the invention, a brief analysis of the magneticdeflection of minority carriers travelling in a semiconductive channelis first presented.

In the preferred embodiments, the novel transducer utilizes an extendedsemiconductive channel having a pair of collectors of minority carrierswhich border on the sides of the channel, and an emitter, or other meansfor injection of minority carriers is disposed at one end of the channelsuch that minority carriers injected into the channel may bepreferentially deflected towards or away from the collectors by amagnetic field.

In such a case, the force acting on the charge q moving at velocity v ina magnetic flux density B which is orthogonal to v F H =vB 10 where theforce F H expressed in terms of an equivalent electric-field as V/cm., vis in cm./sec. and Bis in gauss.

The lateral (i.e., orthogonal to v and B) displacement in the time t is:

5=p,F t =p.L'B 10" where L'=vt is the distance travelled along thechannel in the time t, and if a channel having a length L L' and a widthW between collectors is assumed, we have a transducer efficiency of olw=p.B 10 L'/W. For instance, if p.=l0 cmF/volt sec., B =10 gauss, L'=l0cm and W 10 cm, then 6/W= 10- and consequently, Al 10- I assuming thatthe entire emitter current I is injected into the channel, and AI is thechange in the collector current caused by the magnetic flux.

Of course L, the distance travelled along the channel bounded by twocollectors, can be limited by the bulk lifetime 1, but for narrowchannels bounded by two collectors it is more likely that it will belimited by lateral Brownian motion whereby minority carriers are suckedup by the collector space charge regions. Now since the transit time tfrom the center of the channel to one of its boundaries by Brownianmotion is:

1 IZVI where D is the diffusion constant of the minority carriers whichis related to their mobility by Einstein's law D =p.kT/q when k is theBoltzmann constant and Tthe absolute temperature, if there is noelectric field along the channel the effective length L in the regionbetween the collectors is:

L'-=-'(2Dr) or (ZDI 1/2 whichever is smaller. Thus, L cannot be largerthan about W/2. However, by providing an electric field F along thechannel, the distance travelled becomes L' fLFT0l' L' pFt =F( W/2)/2(kT/q) whichever is smaller.

Thus, using an electric field along the channel, the ratio L/W/2 can bemade larger than unity with corresponding increase in the sensitivity ofthe device. For instance, consider the case of an exponential acceptordistribution in a p-type channel:

C=C,, exp(x/x,,, where C, is the concentration at the end of the channelwhere minority carriers (-electrons) are injected, and x is the distancealong the channel from this injection point.

Then the built-in field is: I

If the value of L is limited by lateral diffusion of electrons to one ofthe channel boundaries, rather than by bulk recombination, one obtainsby substitution of F into one of the previous equations:

Therefore, the ratio L'lW, which enters the transducer efficiency asoutlined previously, becomes:

L'lWW/8 x,,

In order to maximize this expression, it would appear desirable tochoose x, as small as possible, i.e., to select a steep impuritygradient, However, the impurity gradient has to extend along the entirechannel length L, and the concentration, C at x=L has to be stillsufficiently large to provide a significant doping of the semiconductor,and since:

x,,=L/Ln(C,,/C, one has, L,(lI'/2) Ln (C,,,'C )/2 For C,,=10 CHI-3, C=1O cn1. Ln(C /C )/2 becomes equal to 2.4, i.e., the channel lengthshould be chosen at least 2.4 times the half-width of the channel.

Using the above equations, we may also express the optimized x, in termsof the channel width Was follows:

The denominator is 4.8 for the numerical example chosen. Thus for achannel width of W=l cm. and a dopant concentration at the ends of thechannel as indicated above, one should select x cm. and a channel lengthL of at least l.2 10cm., and for silicon at room temperatures theelectron lifetime r in the p-type channel should be at least (W/2) 2DESsee.

In FIG. 1, a semiconductor body 10 of P-type silicon or the like isprovided with a pair of spaced apart N-type collector regions l2 and 14which form a channel region 16 of the P-type body interposed betweenthem. An injector region 18, in this case an N-type emitter region, isprovided at one end of channel 16 where it extends to the wafer surface20 as shown. Conductive contacts 22 and 24 with appropriate leads 26, 28provide low resistance or ohmic contact to collectors l2 and 14respectively. Contact 30 and lead 32 connect to the injection end ofchannel 16, and contact 34 and lead 36 connect to injector region 18.

For an understanding of the invention, consider that channel 16 has awidth W as measured between opposed collector faces 40 and 42 and alength L, as measured from surface 20 to a point 44 near the bottom ofregions 12 and 14. Then, minority carriers injected from region 18 fiowalong channel 16 to regions 12, 14, or recombine with majority carrierseither in channel 16 or in the semiconductive body beyond the channel.

If a magnetic flux B (not shown) is directed into the paper, that is, amagnetic field is applied substantially perpendicular to thelongitudinal axis of the channel and parallel to the interface 40 and42, the minority carriers will be deflected away from one collectorregion and towards the other depending upon the polarity of the appliedmagnetic field.

In the preferred embodiments, the channel is elongated to increase itslength, and the drift velocity v is increased by an electric fieldprovided in the channel by either a suitable impurity profile or anexternally applied electric bias. The elongated channel is provided inthe structure of FIG. 1 between deep diffused pockets [2 and 14 whichextend to the wafer surface, and a longitudinal channel field is builtin to this structure by providing an impurity distribution in channel 16having large impurity concentration at wafer surface 20 which graduallydiminishes to a low concentration at the channel end 44. Consequently,electrons injected at the end of high impurity concentration (adjacentto region 18) are driven by this field towards the low concentration atend 44 such that drift velocity v is increased.

The structure of FIG. 1 may be made by conventional means, as forexample, by first doping a silicon wafer 10 with acceptor impuritiessuch as boron or the like. For instance, boron may be diffused intosurface 20 from an ambient vapor phase to provide P-type conductionhaving a high concentration at this surface and a gradually diminishingconcentration in the direction of the base of the wafer. Thereafter,spaced apart N-type regions 12, 14 and an N-type injector region 18 areformed in wafer 10 by conventional techniques, for example, by diffusionof donor impurities such as phosphorus or the like through mask openingsinto spaced apart portions of surface 20. Low resistance contact filmsof aluminum or the like, may then be deposited by conventional means onappropriate surface portions, and finally, leads are then provided byany of the bonding techniques commonly employed in the semiconductorarts.

Since regions 12 and 14 are deep regions while region 18 iscomparatively shallow, the former would generally be diffused into wafer10 before the formation of region 18. Of course, the diffusant chosenfor region 18 could also be slow moving as compared to that of regions12 and 14.

A preferred channel length of at least 2.4 times the halfwidth of thechannel is provided in this embodiment by spacing of regions 12 and 14inaccordance with the diffusion constant of the impurities used. Inaddition, the values of X and the dopant concentrations at the ends ofthe channel are made to conform to those indicated in the precedingtheoretical discussion.

As previously indicated, there are inherent restrictions in providing alarge built-in longitudinal field over a long channel, however, theserestrictions can be overcome by generating an electric field from anexternal power source in connection to contacts located at opposite endsof the channel.

In the case of an externally applied channel field, the length L' isrestricted by the saturation drift velocity of minority carriers whichis approached with increasing field F. In the case of silicon, thissaturation velocity is v,=l0 cm./sec. Thus In this estimate, we haveused the diffusion constant for holes at low field conditions whichstrictly does not apply to the hot" electrons flowing at the saturationdrift velocity. Nevertheless, the error thereby introduced is minor anddoes not detract from the fact that large channel length/width ratioscan be employed with externally applied fields.

An externally applied field is provided in the structure of FIGS. 2 and3 by means of an additional contact 50 and lead 52 which connect towafer 10 to permit application of an electric bias to channel 16 from anexternal source (not shown). In these FIGS. parts identical to those ofFIG. 1 are identified by corresponding reference numerals.

Preferably, the unit of FIGS. 2 and 3 are constructed in a mannersimilar to that of FIG. 1 to provide a long narrow channel, however,since a field is externally applied a graded impurity concentration ofchannel 16 is unnecessary. Assuming, a P-type channel (P-type wafer) inthe structure of FIG. 2 contact 50, if positively biased as compared tocontact 30, will act as a source of majority carriers (holes) whilecontact 30 acts as a drain of these carriers, and majority carrier flowfrom contact 50 to 30 proceeds along the dotted line 54.

The majority drain contact 30, preferably surrounds injector region 18and is substantially concentric to it at surface 20. Consequently, thedeepest point of the injector region faces the most positive value ofchannel 16 comparing points along the injector-channel interface, andthe injected electrons are concentrated at the center of the channel.

In contrast to devices having a built-in field, when the field isexternally applied between electrodes located at the channel ends, stepsmust be taken to confine the majority carrier flow to the channel.Hence, it is necessary to completely surround the channel by thecollectors or external boundaries of the semiconductive wafer. This maybe accomplished by making regions 12 and 14 extend around the channel.This can be seen from FIG. 3 wherein regions 12 and 14 substantiallyconform to contacts 22, 24 which they underlie. A small gap 62 and 64are provided at the ends of the collector regions, and these are biasedpositive with respect to the surrounding ptype layer such that the spacecharge layer generated at the collector junctions extends from regions12, 14 to the dotted lines 56 and 58. This space charge layer leaves ap-type opening for the channel 16 (within line 56), but coverscompletely gaps 62 and 64 between the horseshoe-shaped collector regions12, 14. In this manner, channel 16 is laterally pinched off from thesurrounding p-layer 66, yet regions l2, 14 remain insulated from eachother by gaps 62, 64.

The structures illustrated in FIGS. 1-3 provide a vertical channelperpendicular to the wafer surface; however, there are severaladvantages of structures having a horizontal channel parallel to thewafer surface since this provides: (1 access of the channel to a highlylocalized magnetic field, for instance, the field ofthe domains onmagnetic'tape; (2) an elongated channel without the necessity of deepdiffusion of the collector regions; (3) other means of collectinginjected minority carriers than the use of reverse biased pn junctions;and (4) case of providing a lateral impurity profile in the channel.

A structure having a horizontal channel is shown in FIG. 4 which depictsa structure having a p-type channel 70 parallel to the wafer surface 72.In this embodiment, the bulk of wafer 74 is an N-type substrate whichprovides one collector region. Substrate 74 is overlaid by a p-typeepitaxial layer 78 which has an elongated N-type region 76 disposed inupper surface 72. Region 76 provides the other collector, and togetherwith substrate 74 forms a ribbonlike channel 70 from the interposedportion of layer 78. An N-type injector region 80 is laterally spacedfrom region 76 at one end of channel 70, and is positioned betweenregion 76 and a majority drain contact 82 which connects to layer 78. Amajority source contact 84 is provided at the other end of channel 70,and contacts 86 and 88 are provided to regions 76 and 80, respectively.It should be noted that drain contact 82 is, in this case, made negativewith respect to source contact 84 so that majority carrier flow is alongline 90 from contact 84 to 82, and enhances minority carrier flow in anopposite direction through channel 70 from region 80. The minoritycarrier flow in channel 70 is then magnetically deflected to eithercollector 74 or 76 by a magnetic field applied parallel to wafer surface72 and orthogonal to channel flow 90; that is, orthogonal to the planeof the figure.

A built-in electric field can also be utilized in this embodiment toincrease sensitivity. That is, the lateral transit time may be increasedby providing a lateral drift field in the channel which opposes the flowof injected minority carriers toward the channel-collector interface.

The lateral field may be accomplished by providing a concentrationvalley, that is a saddlelike impurity profile, perpendicular to thelongitudinal axis of the channel. For example, the impurityconcentration (e.g., boron concentration) of the gaseous ambient may bedecreased during epitaxial growth of layer 78 and then again increasedto the original level so as to provide the distribution plotted in FIG.5.

In FIG. 5, the impurity concentration is plotted along the ordinatewhile the distance from the channel center is plotted along theabscissa. Herein, points a and 17 represent the channel edges orchannel-collector interfaces 71 and 73 of FIG. 4. This graphicallyillustrates the desired saddlelike impurity distribution having maximaat points c and d, adjacent the channel edges, and a minimum at e whichcorresponds to the channel center.

Hence, between c and d, there is a built-in field which tends to drivemajority carriers away from and minority carriers toward the channelaxis e. Consequently, the applied magnetic force has to overcome thislateral drift field in order to propel minority carriers toward eithercollector.

It should also be understood of course, that a built-in longitudinaldrift field could also be utilized in the parallel channel structure ofFIG. 4, and conversely, the lateral field of FIG. 5 could also beemployed by appropriate construction in the vertical channel structureof FIG. 1.

In another embodiment, shown in FIG. 6, the upper collector is providedby a Schottky barrier contact 92. In this case, region 76 and junction73 of .FIG. 4 is replaced by metallic layer 92 which is deposited onsurface 72 in accordance with well known methods of preparation. Forexample, a thin layer of chromium may be deposited on surface 72 of thep-type layer 78 to provide the Schottky barrier contact. This thenprovides a channel portion 70 of epitaxial layer 78 interposed betweencollector substrate 74 and collector 92.

In still another embodiment as shown in FIG. 7, collector region 76 ofFIG. 4 is replaced by an inversion layer 94, induced in the uppersurface of layer 78 by a positively biased metal film 96 which overliesan insulating film 98. For example, a layer of aluminum or the likedeposited over a silicon dioxide film by conventional MOS techniqueswould be suitable.

In this case, contact to inversion region 94 is provided by a connectionto its lateral edge (not shown) or by a lead (not shown) insulativelyextended through film 96 and 98.

In he embodiments shown in FIGS. 4, 6, and 7, the upper collectorregions (76, 92 or 94) and their appropriate contacts may be laterallyextended (that is in a direction into the paper) to provide a thinribbonlike channel, and the extreme edges of the channel can belaterally terminated in each case by the wafer edge or by a pair ofgrooves or the like, cut or etched, in surface 72 parallel-to channel 70and penetrating to collector 74.

The described transducers can also be combined in an integratedarrangement with an amplifying unit, for example by utilizing onecollector as a base region of a bipolar PNP transistor such as thatshown in FIG. 8, or may be combined with an MOS-type unipolartransistor, for example as shown in FIG. 9.

In FIG. 8, the transducer of FIG. 4 is modified by providing a p-typeemitter region 100, formed by diffusion or the like, in upper collector76. In this case, contact 86 is affixed to region 100 so that currentflowing from channel 70 into region 76 must pass through the p-njunction 101 between region 76 and 100. Thus, channel collector 76 canbe made to also operate as the base region of a bipolar PNP transistor106 whose collector is a portion of channel 70.

In operation, contact 86 is connected at 102 to the positive side of avoltage source 104 such that PNP transistor 106 operates in a mannersimilar to contact 84 of FIG. 4, as a source of holes in channel 70.Consequently, the input to transistor 106 is partly controlled by thecollector current of the transducer. Drain contact 82 is also connectedin common to injector contact 88 at 108 and then over a load resistance110, such as a 5 kilo ohm resistor, to the negative terminal of source104 as shown.

Then, the voltage drop caused by the fiow of holes in channel 70 betweentransistor 106 and drain contact 82 provides a slightly negative biasfor the injecting p-n junction 112 since contact 88 of region isconnected to 82. Consequently, minority carriers are injected overjunction 112 into channel 70, and some of them are collected by then-layer 76, thus providing the base current of the transistor 106.Hence, the device has internal feedback, since the minority carriercurrent from channel 70 to collector 76 governs the majority carriercurrent of channel 70 which, in turn, determines the voltage drop in thechannel between junction 112 and contact 82, V

Switching from the on"-state to the ofi-state is provided by magneticdeflection of minority carriers away from the collector region 76.However, for some applications, it is also desireable to provide anadditional majority carrier source contact 114 connected over aresistance 116, for example 50 kilo ohms, to the positive terminal 102of the battery. In this case, there will be a finite channel current andsome limited injection overjunction 112, although the transistor 106might still be off due to magnetic deflection of most of the electronsaway from the collector 76. Reversal of the polarity of the magneticflux can trigger such a device into the on-stage of transistor 106thereby providing greatly enhanced power through load resistor 110.

FIG. 9 shows a further arrangement whereby the transducer illustrated inH6. 4 is modified such that the current change to collector 76 isamplified by an MOS-transistor 120. Herein, transistor 120 consists ofan n-type region 122 whose surface is partially covered with aninsulating film 124 and an overlying gate contact 126.

A p-type region 128 is disposed within region 122 and spaced away fromcollector 76. Region 128 provides a conventional MOS source region oftransistor 120 and is connected through a resistor 123 to gate 126 andregion 76. Resistor 123 and region 128 are connected, in turn, to thepositive side ofa voltage source 132.

Injector region 80 and contact 82 are connected in common through loadresistor 110 to a ground tenninal 138 and the negative side of voltagesource 132. As in the structure of FIG. 8, source terminal 114 isconnected to voltage source 132 over resistor 116, and finally an outputterminal 140 is provided in connection to load resistor 110 as shown.This provides a voltage output between terminal 140 and ground 138.

A sufficiently large negative bias voltage is applied against region 122by means of the positive voltage of gate electrode 126 which causes ap-inversion layer to form at the interface between region 122 andinsulator 124, thereby providing an inversion conductance between thep-pocket 128 and the terminal end 142 of the p-channel 70. The negativebias to region 122 results from electron current flow from channel 70into collector 76 which, in turn, flows over register 123 to thepositive terminal of battery 132.

Again, as in the structure of FIG. 8, we have an on"-stagc in whichelectron current over junction 112, magnetically directed to collector76, causes a gate bias which turns on MOS-transistor 120. This, in turn,provides the hole channel current along dotted line 144 causingincreased electron injection from region 80. In the off-stage, with noelectron collection by region 76 (due to the magnetic field) transistor120 is turned off, and little or no electron injection from region 80 ispresent.

The described devices can of course be utilized in many differentapplications. For example, the structures shown in FIGS. 8 and 9 aresuitable for use in switching applications such as for a magneticallyactivated light switch, or the like. This may be accomplished by anysuitable arrangement which provides reversal of the magnetic polarityacross the channel. That is, a conventional U-shaped magnet (not shown)may be rotatably mounted over the device so that its field may firstpass perpendicular to the channel in one direction and then made to passin the reverse direction by rotation of the magnet through 180 toprovide off-on states of the switch. Concentration of the magnetic fieldcan also be enhanced by the use of soft iron pole pieces or the likeextended laterally from the sides of the transducer to the magnet faces.Then, rotation of the magnet to bring its opposite poles to bear on thepole pieces provides field reversal and circuit switching.

Many different embodiments are possible, of course. For example, N-typechannels with appropriate collector and injector regions may beemployed. In this case, regions of opposite type to those given in thedescription would also be required for the amplifier portions ofthetransducer-amplifier structures.

In addition, substrate 74 may he an insulative member such as sapphireor the like which provides a supporting base upon which layer 78 may beepitaxially deposited, for example. In this embodiment the channel issandwiched between one collector and an insulating means.

Semiconductive materials other than silicon may also be employed. Boththe built-in and externally applied channel field may be utilized, andmany different embodiments of the transducer-amplifier structure may bepossible.

Consequently, many different embodiments are possible without departingfrom the spirit and scope of the invention, and it should be understoodthat the invention is not to be limited except as in the appendedclaims.

lclaim:

1. A semiconductive magnetic transducer comprising an elongatedsemiconductive channel, means disposed at one end of said channel forgeneration and injection ofa constant flow of minority carriers therein,at least one region for collection of minority carriers contiguous witha side ofsaid channel that is substantially parallel to the flow ofminority carriers and of opposite conductivity type from said channel,wherein a magnetic field will deflect said drifting minority carriersthereby affecting their collection in said collector region, and anonvariable electric field provided within said channel by a graduallydecreasing concentration of impurities from the injection end of saidchannel to the opposite end thereofimparting a drift to said minoritycarriers along the axis ofsaid channel and away from the point ofinjection such that the natural drift velocity of the injected minoritycarriers within the channel is substantially increased therebypermitting a corresponding increase in sensitivity for the transducer.

2. The transducer of claim 1 including a lateral variation in impurityconcentration having a saddle-shaped concentration provided by animpurity distribution of gradually decreasing concentration from thechannel sides towards its axis.

3. The transducer of claim 1 including at least one other region forcollection of minority carriers, said other collector region also beingcontiguous with a side of said channel and spaced from said onecollector region.

4. The transducer-amplifier of claim 3 wherein said collector regionsextend around said channel and are spaced apart a short distance attheir ends, and said collector regions are biased electrically againstsaid channel to an extent that the space charge layers between saidcollectors and channel extend across the spacing between said collectorsso that the channel is fully surrounded by said collectors and theirspace charge regions.

5. A semiconductive magnetic transducer-amplifier comprising incombination a body of semiconductive material; a semiconductive channeldisposed within said body; at least one collector region ofsaid bodyadjoining said channel and of opposite conductivity type from saidchannel; means to inject minority carriers into said channel from anemitter located at said surface at one end of said channel in order thatminority carriers moving along said channel can be deflected to saidcollector by a magnetic field applied to said channel; and anenhancement MOS transistor disposed adjacent said channel with itsinversion layer in series connection therewith, and said collectorregion being coupled to the gate of said transistor and biased inaccordance with the flow of minority carriers into said collector suchthat said MOS transistor operates as a source of majority carriers tosaid channel.

6. The transducer of claim 5 wherein said MOS transistor includes afirst region of the same conductivity type as said collector region,said first region spaced apart from said collector and disposed in saidchannel at the opposite end from said injection region, said firstregion having a majority source region disposed therein, said majoritysource region being spaced away from said collector region, saidtransistor having a gate electrode overlying and insulatively spacedfrom said first region, said gate overlying a portion of said firstregion which is disposed between its source region and said collectorregion, said collector region coupled to said gate electrode, and saidminority flow into said collector providing a bias of said gateelectrode which inverts the underlying region such prising incombination a body of semiconductive material; a

semiconductive channel of opposite conductivity type from said body anddisposed within said body so as to be contiguous with said body along asubstantially planar surface; a collector region of oppositeconductivity type from said channel and contiguous with the outsideplanar surface of said channel,

means to inject minority carriers into said channel from an emitterlocated at the surface at one end of said channel; a source of majoritycarriers located at the surface at the other end of said channel;circuit means to provide a flow of majority carriers along said channelfrom said source of majority carriers toward said emitter of minoritycarriers, thereby generating a drift field along said channel so thatminority carriers drifting along said channel are deflected to saidcollector by a magnetic field applied to said channel; and an emitterregion within said collector and of opposite conductivity type from saidcollector, which together with said collector and said channel forms abipolar transistor such that the output of said transistor amplifieroperates as a source of majority carriers for said channel and isproportional to minority carrier flow deflected to said channel.

9. The transducer-amplifier of claim 8 including means for controllingthe injection of minority carriers into said channel in accordance withsaid majority carrier flow thereby providing a bistable device havingone state characterized by a comparatively large minority carrier flowand another state of little minority carrier flow in said channel.

10. The transducer of claim 9 including a magnetic field in saidchannel, said magnetic field directed across said channel so as tocontrol minority flow into said collector, and means for varying saidmagnetic field to control said minority flow into said collector andthereby switch said bistable device from one state to the other.

11. The transducer-amplifier of claim 9 wherein said channel includes asource and a drain of majority carriers, said majority carrier drainbeing located at the injection end of said channel, said injection meansbeing disposed between said drain and said collector, and said injectionmeans being conductively connected to said drain so as to controlminority carrier injection in accordance with majority carrier flow.

2. The transducer of claim 1 including a lateral variation in impurityconcentration having a saddle-shaped concentration provided by animpurity distribution of gradually decreasing concentration from thechannel sides towards its axis.
 3. The transducer of claim 1 includingat least one other region for collection of minority carriers, saidother collector region also being contiguous with a side of said channeland spaced from said one collector region.
 4. The transducer-amplifierof claim 3 wherein said collector regions extend around said channel andare spaced apart a short distance at their ends, and said collectorregions are biased electrically against said channel to an extent thatthe space charge layers between said collectors and channel extendacross the spacing between said collectors so that the channel is fullysurrounded by said collectors and their space charge regions.
 5. Asemiconductive magnetic transducer-amplifier comprising in combination abody of semiconductive material; a semiconductive channel disposedwithin said body; at least one collector region of said body adjoiningsaid channel and of opposite conductivity type from said channel; meansto inject minority carriers into said channel from an emitter located atsaid surface at one end of said channel in order that minority carriersmoving along said channel can be deflected to said collector by amagnetic field applied to said channel; and an enhancement MOStransistor disposed adjacent said channel with its inversion layer inseries connection therewith, and said collector region being coupled tothe gate of said transistor and biased in accordance with the flow ofminority carriers into said collector such that said MOS transistoroperates as a source of majority carriers to said channel.
 6. Thetransducer of claim 5 wherein said MOS transistor includes a firstregion of the same conductivity type as said collector region, saidfirst region spaced apart from said collector and disposed in saidchannel at the opposite end from said injection region, said firstregion having a majority source region disposed therein, said majoritysource region being spaced away from said collector region, saidtransistor having a gate electrode overlying and insulatively spacedfrom said first region, said gate overlying a portion of said firstregion which is disposed between its source region and said collectorregion, said collector region coupled to said gate electrode, and saidminority flow into said collector providing a bias of said gateelectrode which inverts the underlying region such that said sourceregion injects majority carriers through said inverted region into saidchannel.
 7. The transducer-amplifier of claim 7 wherein said channelincludes a source and a drain of majority carriers disposed at opposingends of said channel, said majority carrier drain being located at theinjection end of said channel, said injection means being disposedbetween said drain and said collector, and said injection means beingconductively connected to said drain so as to control minority carrierinjection in accordance with majority carrier flow.
 8. A semiconductivemagnetic transducer-amplifier comprising in combination A body ofsemiconductive material; a semiconductive channel of oppositeconductivity type from said body and disposed within said body so as tobe contiguous with said body along a substantially planar surface; acollector region of opposite conductivity type from said channel andcontiguous with the outside planar surface of said channel, means toinject minority carriers into said channel from an emitter located atthe surface at one end of said channel; a source of majority carrierslocated at the surface at the other end of said channel; circuit meansto provide a flow of majority carriers along said channel from saidsource of majority carriers toward said emitter of minority carriers,thereby generating a drift field along said channel so that minoritycarriers drifting along said channel are deflected to said collector bya magnetic field applied to said channel; and an emitter region withinsaid collector and of opposite conductivity type from said collector,which together with said collector and said channel forms a bipolartransistor such that the output of said transistor amplifier operates asa source of majority carriers for said channel and is proportional tominority carrier flow deflected to said channel.
 9. Thetransducer-amplifier of claim 8 including means for controlling theinjection of minority carriers into said channel in accordance with saidmajority carrier flow thereby providing a bistable device having onestate characterized by a comparatively large minority carrier flow andanother state of little minority carrier flow in said channel.
 10. Thetransducer of claim 9 including a magnetic field in said channel, saidmagnetic field directed across said channel so as to control minorityflow into said collector, and means for varying said magnetic field tocontrol said minority flow into said collector and thereby switch saidbistable device from one state to the other.
 11. Thetransducer-amplifier of claim 9 wherein said channel includes a sourceand a drain of majority carriers, said majority carrier drain beinglocated at the injection end of said channel, said injection means beingdisposed between said drain and said collector, and said injection meansbeing conductively connected to said drain so as to control minoritycarrier injection in accordance with majority carrier flow.